The development of the imaginal disc of Drosophila is organized into discrete units referred to as compartments (developmental compartments). Each compartment is founded by a group fo cells (polyclone) whose developmental fates become specified by the compartmentalization process. Very little is known about how the compartments are formed but the fact that their formation is dependent on a group of cells would seem to indicate that cell-cell interactions must play an important role in this process. From previous tudies inthe ouse embryo, we have observed the presence of communication compartments-that is a group of cells that communicate well with one another but not with cells outside of the compartment boundary. It would be interesting to consider the possibility that perhaps gap junctional communication compartments may mediate the formation of developmental compartments in imaginal discs. The aim of this proposal is to characterize the gap junctional communication propertiesof the wing disc and determine if gap junctional communication compartments are present. If gap junctional communication compartments are involved in the formation of developmental compartments, then the boundaries of both sets of compartments should be coincident. The communication properties of the wing imaginal disc will be characterized with microelectrode impalements to measure the extent of ionic and dye coupling. These measurements will reveal the presence of any communication compartments. In conjunction with the ionic and dye coupling measurements, electron microscopic morphometric measurements will be made to determine the number and size of gap junctions present in the wing disc. This analysis should reveal if a reduction in the number of junctonal channels at a compartment boundary could explain the basis for the formation of communication compartments. It is hoped that this study may lead to a better understanding of the mechanisms which regulate cell differentiation and development.